Amplifying arrangement comprising tunable circuits



2,088,034 AMPLIFYING ARRANGEMENT COMPRI$ING TUNABLE cmcuns H. RlNlA Fi led June 16, 1934 July 27, 1937.

INVENTOR HER/PE ATTORNEY Patented July 27, 1937 UNITED STATES PA FFICE Herre Rinia, Eindhoven, Netherlands, assignor to Radio Corporation of Delaware of America, a corporation Application June 16, 1934, Serial No. 730,882

- In the Netherlands June 21, 1933 2 Claims.

This invention relates to amplifying arrangements having a plurality of tunable circuits which are so arranged that part of the coils can be short circuited for the reception of short waves.

The invention consists in that with one or more of the tunable circuits a condenser is inserted in the line through which part of the coil can be short circuited.

The advantages thus obtained are as follows:

When a plurality of quite similar tunable circuits are provided in a cascade arrangement the resulting resonance curve of the amplifier will become comparatively sharp in the short wave range, due to which distortion will occur when amplifying the high tones. 1

By inserting a condenser in one or more of the circuits, if the latter are adjusted to the reception of short waves, said circuits will be slightly detuned with respect to the other circuits present in the amplifier. Owing to this. the resulting frequency band becomes slightly wider and the high tones are amplified to the same degree as the low tones.

Another advantage of the circuit arrangement according to the invention is achieved if a band filter instead of an ordinary L-C circuit be inserted in the grid circuit of one or more of the tubes. When in this case the capacity of the tuning condensers and the coils of the circuits of which the band filters are rendered equal to those of the simple LC circuits, then the magnitudes of the band filters and those of the other circuits will still differ due to the coupling capacities present in the band filter circuits. By interposing in the manner set out above a condenser in the simple circuits, the magnitudes of the band filters and of the simple circuits can be equalized at least for the short wave range.

The invention is illustrated in the accompanying drawing in which Fig. 1 is a circuit diagram of one application of the invention and Figs. 2 and 3 are modifications, thereof.

Fig. 1 shows a multi-stage amplifying system adapted for the amplification of long or short waves. For the reception of short waves the switches S are closed thus short circuiting parts of the inductances L. In accordance with the invention a condenser C is inserted in one stage in the lead that short circuits the part of the inductance not used for short wave reception. The condenser C is not in the circuit when long waves are received, but is connected in series in the circuit for short Wave reception. That circuit is thereby detuned slightly with respect to the circuit in the other stage. Condenser C is made to have reactance of the order of magnitude of the circuit resistance. This detunes the 5 first tuned circuit slightly with respect to the second tuned circuit thereby producing staggered tuning and consequently a wider band of transmitted frequencies and hence improves high frequency response.

In Figs. 2 and 3 the first stage of the cascade arrangement has a band. pass filter in place of a simple tuned circuit. The type of band pass filter illustrated in Fig. 2 requires that the additional condensers C be added in the filter whereas the type of band pass filter illustrated in Fig. 3 requires that the additional condenser be added in the following stages.

What I claim is:

1. A mu1ti-range tunable circuit comprising an inductance and a variable condenser connected in shunt thereto adapted to be tuned over a certain frequency band, said inductance being divided into portions by a tap connection, a condenser having one side connected to one end of the inductance and to one side of the variable condenser, and switching means connecting the other side of said condenser to said tap connection whereby that portion of the inductance between the tap connection and the first mentioned side of the condenser is short circuited only by said condenser for the reception of a different frequency band, the remaining active portion of the inductance together with the variable condenser and the second condenser, each connected together in series, forming a circuit which is tunable to said different frequency band.

2. A plurality of cascade-connected tunable circuits, successive ones of said circuits being intercoupled by means of a vacuum tube, means associated with each of the tunable circuits for short-oircuiting a portion of the inductance thereof for the reception of short-waves, at least one of said short-circuiting means including a series condenser which is connected across the short-circuited portion of the inductance for detuning the associated tunable circuit in the reception of short waves, said condenser otherwise not being included in the tunable circuit.

HERRE RINIA. 

